1. Field of the Invention
The invention relates to image forming apparatus and, more particularly, to an apparatus which can be used as a machine dedicated to the formation of a single-color image by allowing a plurality of development cartridges containing toners in the same color to be mounted in place of development cartridges containing toners for forming a color image.
2. Description of the Related Art
Image forming apparatus employing an electrophotographic recording method have been known, in which an electrostatic latent image is exposed on a surface of a carrying member fabricated from a photosensitive material. In such image forming apparatus, a toner image developed from such an electrostatic latent image using toners and carried on a surface of the carrying member is transferred onto a recording medium such as recording paper to form an image. The electrostatic latent image is developed using a toner by rotating a development roller facing the surface of the carrying member to cause a toner on a surface of the roller to transfer and stick to the carrying member. The toner is supplied to the development roller from a supply roller which is pressed against the development roller while rotating in a toner containing space.
Image forming apparatus employing the electrophotographic recording method include apparatus configured to accommodate a plurality of development cartridges in a rotary unit, the cartridges having a development roller which faces a carrying member and a container which contains a supply roller and a toner. In such an image forming apparatus, a development cartridge in a developing position facing the carrying member can be switched to another by rotating the rotary unit around a rotary shaft.
Therefore, when such an image forming apparatus is configured to allow development cartridges containing toners in yellow (Y), magenta (M), cyan (C), and black (K), respectively, to be accommodated (mounted) in the rotary unit as development cartridges for applying toner on a surface of a carrying member, a color image can be formed by switching the development cartridges sequentially to apply the colors one over another.
In the case of such an electrophotographic recording type image forming apparatus, there is a need for refreshing the toners in the containers by agitating the same to maintain image quality. Therefore, some image forming apparatus with a rotary unit have a configuration in which the toners in the containers can be temporarily agitated to be refreshed by rotating the rotary unit to turn the development cartridges upside down after a predetermined amount of image is formed.
Specifically, in such an image forming apparatus, the development cartridges are sequentially switched to form a color image. Therefore, image quality can be maintained as occasions demand by refreshing the developing toners concurrently with an operation of switching development cartridges in which the rotary unit is rotated to cause a development roller to face the carrying member.
However, when a single-color image is formed, one development cartridge is continuously used, and the operation of causing one rotation of the rotary unit may be required during the continuous image forming operation (developing operation). Since the operation of causing one rotation of the rotary unit takes time and can interrupt an image forming operation, an agitator may be provided in a development cartridge to refresh a toner therein by agitating (conditioning) it. However, when such an agitator is also provided in development cartridges containing toners which are less frequently used for forming single-color images, there will be a wasteful cost increase. For this reason, there are suggestions for the provision of an agitator only in a development cartridge containing a toner in black (K) which is frequently used for forming single-color images such as documents (see JP-A-2003-255662 for example).
In some image forming apparatus having a rotary unit, a partition plate is provided in a development cartridge (container) to define a small space in which a supply roller is to be rotated, and the development cartridge is turned upside down after a predetermined amount of image is formed to perform an operation of temporarily agitating (refreshing) the toner in the container and replenishing (conditioning) the space in which the supply roller rotates with the toner.
In such an image forming apparatus, when a color image is formed, development cartridges are sequentially switched, and the operation of replenishing the spaces in which the supply rollers rotate with toners is performed concurrently with a development cartridge switching operation even before the toner in any of the development cartridges runs out.
Under the circumstance, even for such a development cartridge having a partition plate, there is a need for providing a replenishing device for replenishing the supply roller with the toner without relying on the rotation of the cartridge when the development cartridge is frequently used for forming single-color images.
There are suggestions on configurations to allow a plurality of development cartridges containing toners in the same color (which is black in most cases) to be mounted in such an image forming apparatus having such a rotary unit. In such configurations, the rotary unit is rotated to switch the development cartridges sequentially each time the toner in the cartridge in use runs out, which makes it possible to continue the formation of single-color images for a long time while reducing the number of times of an operation of replacing the development cartridges to replenish the apparatus with the toner (see JP-A-2002-351190 and JP-A-2003-316106, for example).
However, in the case of an image forming apparatus in which only development cartridges containing a toner for single-color images incorporate a device for a conditioning operation to agitate and re-supply the toner contained therein, when development cartridges containing toners in the same color are to be mounted in all housing positions, ease of use is reduced if there are restrictions on the housing positions for the development cartridges depending on whether they have an agitator or not. On the other hand, when all of the development cartridges containing the toners in the same color are equipped with an agitator, the amount of the toner contained is reduced because the spaces to contain the toner include the members some of which cannot be operated.